In particular, the display case can simply enclose the works, preventing them from being touched by people or things, or it can be such as to ensure that the works are conserved in a protected environment; here and hereafter by protected environment we means an environment in which the atmosphere is controlled, by monitoring one or more parameters from temperature, humidity, dust content, pollutant content, in order to maintain the foreseen conservation conditions of the objects displayed, and wherein unauthorised personnel are denied the possibility of access, in order to prevent theft or damage of the displayed objects.
Display cases of this type must therefore satisfy various kinds of requirements, in relation to the conservation and integrity of the displayed objects. Moreover, of course, these display cases must ensure the best visibility of the objects displayed.
Therefore, the systems for fastening the fixed parts together are very important, in order to ensure the essential solidity of the display case.
In order to improve visibility, the manufacturers of display cases try as much as possible to use transparent materials—typically glass—for the walls of display cases. As well as ensuring the best visibility of the objects displayed, the widespread use of glass is often desired by designers of display cases because the transparency of the material allows the displayed objects to be have the maximum visual impact.
Display cases have thus been developed with a base block having a casing formed from panels on top; the base block houses all of the technical components that may be necessary to ensure that the environment inside the casing is protected and is therefore normally closed by non-transparent walls, which conceal all of the technical components from view; vice-versa, the walls of the casing are made entirely or partially from glass, for the aforementioned reasons.
The casing can be made from walls of transparent material all fastened together, so as to form a bell that is lifted from the base block to gain access inside the display case. Otherwise, some walls (fixed walls) are fastened to the base block and together while one or more walls (openable walls) are mobile, thanks to suitable opening mechanisms.
In order to fasten together fixed walls made from transparent material, it is normal to glue together the walls through suitable adhesives, along adjacent peripheral edges, mostly cut to 45°.
Thanks to modern adhesives, it is possible to ensure excellent stability and safety of the gluing. However, sometimes it is still possible for anomalous, unpredictable or in any case unforeseen conditions to lead to lower solidity of gluing than expected. This can happen for example because in the gluing step there was some anomalous and not necessarily detectable condition, which can (immediately or perhaps some time later) lead to a reduction in the adhesion between the glued walls. Or else it is possible for particular environmental conditions (in terms of temperature, humidity, exposure to light or to atmospheric agents) over to modify (worsen) the adhesion characteristics of a gluing even carried out as recommended.
In these cases, the display case will be exposed to the risk of the walls becoming unstuck and therefore collapsing. This is a risk that often cannot be accepted, however small it may be, due to the delicacy and value of the works intended to be housed in the display case, which could be irredeemably damaged in the case of collapsing of the display case.
For this reason, in the case of display cases intended for delicate and/or very high value works, display cases of this type, with almost completely transparent walls, are often not used, even though this impairs visibility.